耗散费米子动力学中的分岔
Bifurcations in dissipative fermionic dynamics
摘要：
玻尔兹曼-朗之万单体模型（Boltzmann-Langevin One-Body Model，BLOB）是一种基于三维玻尔兹曼-朗之万方程解的新的单体输运方法;它用于处理大振幅相空间涨落，并对耗散费米子动力学具有广泛的适用性。研究了费米能级下重离子碰撞动力学轨迹中分叉现象的发生。该模型，适用于在这种碰撞中形成的稀释系统，揭示了更接近观察比以前的尝试，包括在玻尔兹曼理论中的朗之万项。动力学轨迹中的分叉和双峰行为的发生决定了碎片形成机制。特别是，在阈值附近，两个能量上有利的机制之间的波动突出，使得当从相同的入口通道演化时，可以访问各种出口通道。这一描述给出了费米能下抑制重离子碰撞的两种阈值情形的定量指示。第一，中心碰撞中的融合到多重碎片的阈值，在这种情况下，系统要么恢复到紧凑的形状，要么分裂成几个大小相似的碎片。第二，从二元机制到颈部碎裂（一般来说，三元通道）的过渡，在外围碰撞。
英文摘要：
The Boltzmann-Langevin One-Body model (BLOB), is a novel one-body transport approach, based on the solution of the Boltzmann-Langevin equation in three dimensions; it is used to handle large-amplitude phase-space fluctuations and has a broad applicability for dissipative fermionic dynamics. We study the occurrence of bifurcations in the dynamical trajectories describing heavy-ion collisions at Fermi energies. The model, applied to dilute systems formed in such collisions, reveals to be closer to the observation than previous attempts to include a Langevin term in Boltzmann theories. The onset of bifurcations and bimodal behaviour in dynamical trajectories, determines the fragment-formation mechanism. In particular, in the proximity of a threshold, fluctuations between two energetically favourable mechanisms stand out, so that when evolving from the same entrance channel, a variety of exit channels is accessible. This description gives quantitative indications about two threshold situations which characterise heavy-ion collisions at Fermi energies. First, the fusion-to-multifragmentation threshold in central collisions, where the system either reverts to a compact shape, or splits into several pieces of similar sizes. Second, the transition from binary mechanisms to neck fragmentation (in general, ternary channels), in peripheral collisions.
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